1. Field of the Invention
This invention relates to a ceramic-metal composite article and fabrication method therefor. In particular, the invention relates to a system comprising a composite braze joint structure for joining members having very dissimilar coefficients of thermal expansion. Furthermore, the present invention relates to a composite braze joint for joining a metal and a ceramic member.
2. Description of the Prior Art
A major problem in joining ceramics to metals is the thermal mismatch between the ceramic and metal materials. Thermal mismatch causes significant residual stress in the ceramic, leading to catastrophic failure of the joint. It is well known that to join materials having markedly different coefficients of thermal expansion and still provide a strong joint it is necessary to implement a means for reducing the strain which builds at the joint as the joined members cool. Ceramic-metal joints have used various joining methods, e.g. glass frit, diffusion bonding, brazing, and mechanical shrink fit, and various joint geometries, e.g. butt, conical, and cylindrical joint geometries.
One technique used is to join the materials at as low a temperature as possible. Active brazing alloy has heretofore been used for joining a ceramic member and a metallic member of a composite assembly. An example of such a composite assembly having been practically used, is a compression rotor for a turbocharger. The active brazing alloy is used exclusively with a view to increasing the strength at the joint between the ceramic member and the metallic member. In using such a brazing alloy, a reaction layer is formed between the brazing alloy and the ceramic member to firmly bond the same and thereby enable the ceramic member and the metallic member to be joined firmly. Further, among active brazing alloys, low melting point brazing alloys (solidus point is from 600xc2x0 C. to 750xc2x0 C.) such as Inxe2x80x94Cuxe2x80x94Agxe2x80x94Ti brazing alloy are used for joining the members of a mechanical part assembly for an automobile engine, with a view to reducing the difference in shrinkage (thermal distortion) between the ceramic and metallic members due to the difference in thermal expansion coefficient therebetween.
According to one aspect of the present invention, there is provided a brazing system for joining members, wherein at least one of which is a metallic member, and wherein another is a ceramic member.
It is an object of the present invention, therefore, to provide an brazing system for joining individual constituent members, wherein at least one of which is a metallic member and wherein another is a ceramic member, an itself providing a high strength joint in spite of large differences in coefficients of thermal expansion between the joined members.
It is yet another object of this invention to provide a means for overcoming large mechanical stress is caused by joining materials having large differences in coefficients of thermal expansion.
It is a further object of the present invention to provide a composite assembly which is joined by using a composite brazing alloy.
It is still another object of the present invention to provide a braze assembly which is capable of absorbing mechanical strain generated when joining materials having dissimilar thermal characteristics.
These and other objects will become evident to those having skill in these arts as the invention is described below.